The tent, inaugurated at a ceremony on Thursday, stands in the garden of the former St Ethelburga's Church, which was destroyed by an Irish Republican Army (IRA) bomb in 1993.
It was rebuilt and Charles, the heir to the British throne, inaugurated it as a centre for peace and reconciliation in 2002.
Charles told his interfaith audience seated in a circle inside the rainproof tent that there was a need for understanding as different religions attempt to "explain the nature of mystery".
"We are all trying to explain the nature of mystery and in a sense it is almost impossible to explain," he said.
"If only we could understand each other's groping to understand the mystery, not try to overdo the way in which we decide that we know everything, we might perhaps reduce the level of conflict and violence and misunderstanding."
Attending the event were the bishop of London, Right Reverend Richard Chartres, Britain's chief rabbi, Sir Jonathan Sacks, and representatives of the Baha'i, Buddhist, Jain, Zoroastrian, Hindu, Sikh and Muslim faiths.
Desmond Tutu, the former archbishop of Cape Town, South Africa, and the 1984 Nobel Peace Prize winner, Bill Clinton, the former US president, and U2 front-man Bono all sent messages of support.
The tent will host events promoting interfaith dialogue as well as music, poetry and story-telling.